The role of feed protein quality in reducing environmental pollution by lowering nitrogen excretion. II. Choice of an assay for monitoring protein quality and predicting protein utilization.

The optimum protein nutrition of farm animals allowing minimum nitrogen excretion is a compromise between performance (weight gain) and efficiency of protein utilization. The use of highly digestible feed ingredients allowing maximum nitrogen retention requires assay techniques which are suitable for monitoring protein quality of the feed or predicting nitrogen utilization of the animal. The various assay methods reflecting the protein metabolism of the animal may give different information according to the criteria, which they utilize. Therefore, a suitable assay should be selected with care, depending on the question to be answered. The various aspects of selecting assays for monitoring the protein quality of feeds and predicting protein utilization by the animals are discussed.